The Riley 12/4, or from 1936 the Riley 1½-litre, is a range of cars made from 1935 to 1938 by the British Riley available with saloons, tourers, and sports/racing coachwork.

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Riley in the 30s

British manufacturer Riley enjoyed considerable racing success during the 1930s, proving itself a worthy competitor to Bentley, Aston Martin, and HRG at hillclimbs and rallies. A factory-entered Riley finished 3rd at Le Mans in 1934, by which time a diverse array of racing roadsters had emerged from the manufacturer, including the Brooklands, the Ulster TT, and the MPH Sprite.

Among these two-seaters was the Imp, a 9hp model first introduced as a road car in late 1933. The Imp took the checkered flag at its competition debut during the 1934 Scottish Rally, and showed great promise at the more competitive 1934 Ulster Tourist Trophy, where an all-Imp factory contingent netted 9th, 11th, 12th, and 16th-place finishes. 

Meanwhile, at the 1934 Olympia Motor Show Riley announced its 1935 model line, including the introduction of the company's first new 4-cylinder engine in seven years, the 1.5-liter 12/4. The platform included a new bodystyle on a longer wheelbase, the Falcon saloon. As elegant as the Falcon's swept coachwork was in comparison to other mid-market British sedans, many enthusiasts still chose to modify the car into a lightweight competition roadster, for which the more powerful 12/4 motor was particularly suited.

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Engineering

The car is powered by a four cylinder 1496cc "12/4 Engine" with one or two Zenith carburettors. Designed by Hugh Rose it was based on the Riley 9 engine but with some significant changes including the cylinder block and crankcase being cast as one unit. It was advanced for its day with twin camshafts mounted high in the engine block, cross flow head on some versions, and Zenith or twin SU carburettors. Production of the engine continued until 1955 and also powered cars sold under these model names in these model years:

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• Riley 12 1939 to 1940

• Riley RMA and then Riley RME 1946 to 1955

• Riley One-Point-Five 1957 to 1965 used a BMC B series engine

 

The chassis had half-elliptic leaf springs all round and drive was to the rear wheels through either a four speed preselector or manual gearbox.  Girling rod brakes were fitted. Three different wheelbases were made and two track options of 48 in (1,219 mm) on most versions or 51 in (1,295 mm) on the 1936 Adelphi, Continental and Kestrel saloons.

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Coachwork

At launch three body styles were available: the Kestrel 4 light fastback saloon, the Falcon saloon and the Lynx open tourer. In 1936 the Kestrel became a six light, the Falcon was replaced by the Adelphi six light saloon and the Continental touring sallon was introduced.

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